Method for measuring the basic amount in basic aluminum sulfate solution for removal of SO2 gas

Abstract

Reaction heat values of basic aluminum sulfate solution with acid such as sulfuric acid are correlative with an amount of base contained in said solution. The difference of temperatures of said solution before and after its reaction with said acid is utilized as an indication for the calibration of the basic amount in the solution. This calibration is effectively utilized for the control of the basic amount of said solution which is employed in the removal of SO2 gas from a waste gas.

What is claimed is: 
     
       1. A method for removing SO 2  from a waste gas comprising: (1) contacting the waste gas with a basic aluminum sulfate solution which absorbs the SO 2  from the gas;   (2) subjecting the solution with the absorbed SO 2  gas therein to oxidation to convert any sulfite ion to sulfate;   (3) returning a major portion (P 1 ) of the oxidized solution to the absorbing step;   (4) neutralizing the remainder of the oxidized solution with calcium carbonate or calcium hydroxide to precipitate gypsum which is separated to produce solution (P 2 );   (5) returning solution (P 2 ) to the absorbing step; and controlling the amounts of basic aluminum sulfate at desired levels in solutions P 1  and P 2  by   (a) obtaining samples of solutions P 1  and P 2     (b) measuring the temperatures T 1  and T 1'  of the sample solutions P 1  and P 2 , respectively;   (c) adding sulfuric acid to each of sample solutions P 1  and P 2  in amounts at least equivalent, on a stoichiometric basis to the estimated basic amount in each solution and immediately measuring the respective temperatures T 2  and T 2'  of the mixtures;   (d) determining the basic amount for each respective solution from the temperature differences T 1  and T 2 , and T 1'  and T 2'  from a predetermined calibration curve of the linear relationship of temperature difference and basic amount; and   (e) adjusting the basic amounts in solutions P 1  and P 2  to the desired levels based on said determination.   
     
     
       2. The method of claim 1 in which the basic amount thus determined is related to basicity of solutions P 1  and P 2  by the expression ##EQU3## and the basicity of solution P 1  is kept at not less than about 5% and the basicity of solution P 2  is kept at not more than about 40%. 
     
     
       3. The method of claim 1 or 2 wherein an electric current is generated in dependence on the respective temperature differences, the electric current being related to a predetermined calibration and determining said basic amount therefrom. 
     
     
       4. The method of claim 1 or 2 wherein the sulfuric acid concentration is between about 3 to 8 N. 
     
     
       5. The method of claim 1 or 2 wherein the sulfuric acid concentration is between about 4 to 5 N.